<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .content{width: 100%;}

    .o {
        background-image: url(../响应式/img/上.png);
        background-repeat: no-repeat;
        margin: 10px;
        background-size: 100% 100%;
        width: 100%;
        height: 100px;
    }

    .i {
        margin: 10px;
        display: grid;
        grid-template-columns: 33.33% 33.33% 33.33%;
        grid-template-rows: 33.33% 33.33% 33.33%;
    }
    .i div{background-color: darkgrey;
            box-sizing: border-box;
            border: 5px white solid;
            height: 300px;
    }

    .d {
        background-image: url(../响应式/img/下.png);
        background-repeat: no-repeat;
        margin: 10px;
        background-size: 100% 100%;
        width: 100%;
        height: 100px;
    }
</style>

<body>
    <div class="content">
    <div class="o"></div>
    <div class="i">
        <div class="one"></div>
        <div class="two"></div>
        <div class="three"></div>
    </div>
    <div class="d"></div>
</div>
</body>
</html>